Protein kinase C modulates the insulin-stimulated increase in Akt1 and Akt3 activity in 3T3-L1 adipocytes.
In the present studies, we have compared the properties of two members of the Akt family of ser/thr kinases, Akt1 and Akt3. First, we demonstrate that both 3T3-L1 fibroblasts and adipocytes express Akt3 mRNA by RT-PCR and sequencing of the resultant PCR product. Second, we show that insulin stimulates the enzymatic activity of Akt1 and Akt3 15- and 7-fold, respectively. We then investigated the ability of protein kinase C to regulate Akt1 and 3. Neither enzyme was activated by stimulation of protein kinase C, however, the insulin-stimulated increases in activity of both isozymes were found to be comparably inhibited by prior protein kinase C activation. Since this inhibition could have resulted from an interaction of the pleckstrin homology domain of the Akt with protein kinase C, we also examined the ability of a mutant Akt1 lacking this domain to be regulated by this enzyme. The insulin-stimulated increase in enzymatic activity of this mutant Akt was regulated by PKC activation like the wild type enzyme. These results indicate that Akt1 and 3 are similarly stimulated by insulin and this stimulation is inhibited by prior activation of protein kinase C through a mechanism that is independent of the presence of the pleckstrin homology domain.
Barthel
A
A
Department of Molecular Pharmacology, Stanford University School of Medicine, California 94305, USA.
Nakatani
K
K
Dandekar
A A
AA
Roth
R A
RA
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects*; D000818:Animals; D004789:Enzyme Activation / Q000502:physiology; D005786:Gene Expression Regulation / Q000235:genetics; D007328:Insulin / Q000494:pharmacology*; D007329:Insulin Antagonists / Q000494:pharmacology; D007333:Insulin Resistance / Q000502:physiology; D051379:Mice; D011493:Protein Kinase C / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007328:Insulin; D007329:Insulin Antagonists; D012333:RNA, Messenger; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate